For example, Patent Document 1 discloses a driving position display device in which, once a vehicle runs on a newly constructed road, data on the road can be stored. This driving position display device determines whether road data corresponding to a trail of running of the relevant vehicle is included in map data or not. When it is not included, the trail of running of the relevant vehicle is stored as configuration of road and road data, and this stored data is displayed on a display device.
Patent Document 1: JP-H9-33267A
Techniques to determine the relevant vehicle position include radio navigation typified by GPS and self navigation in which the relevant vehicle position is measured based on mileage and traveling direction. However, whichever technique is adopted, the obtained relevant vehicle position contains a position-fix error. To cope with this, map matching is generally adopted in conventional automobile navigation systems to enhance the accuracy of the relevant vehicle position. Map matching is based on the assumption that a vehicle absolutely runs on a road. It is a process in which the obtained relevant vehicle position and its trail of running are fit to a road in proximity to the vehicle and the relevant vehicle position is corrected so that it agrees with a point on the most likely road.
However, this technique has a problem. When the relevant vehicle gets from a road contained in road map data onto a road not contained in the road map data, its position can be erroneously map-matched to a road contained in the road map data. For this reason, even when a history of map matching position obtained by map matching is used, road data that departs from the actual configuration of the road can be generated.